Patent documents 1 and 2 listed below disclose conventional direct-current stabilized power supply apparatuses proposed by the applicant of the present invention.
Specifically, the direct-current stabilized power supply apparatus disclosed in patent document 1 includes an error amplifier amplifying the voltage difference between a feedback voltage varying according to an output voltage and a predetermined reference voltage, and switches an output transistor with the output signal (error voltage) of the error amplifier. More specifically, this direct-current stabilized power supply apparatus generates a PWM (pulse width modulation) signal having a duty ratio corresponding to the comparison result between the error voltage Verr and a predetermined slope voltage Vslp (having a slope waveform or a triangular waveform) so as to turn on and off the output transistor with the PWM signal.
In order to respond to rapid load variations more quickly, the direct-current stabilized power supply apparatus disclosed in patent document 2 controls driving of the output transistor by, while monitoring not only the output voltage but also a switch current flowing through the output transistor and a load current flowing through the load, shifting the slope voltage Vslp appropriately according to the result of the monitoring (so-called current mode control).
Patent document 1: JP-A-H07-336999
Patent document 2: JP-A-2004-173353